In the fabrication process of an advanced semiconductor product, the degree of micropatterning is increased by mainly increasing the resolution of an exposure apparatus. The resolution of an exposure apparatus is determined by the wavelength of exposure light and the numerical aperture (NA) of a projection lens. More specifically, it is known well, the shorter the wavelength and the higher the NA, the higher the resolution. Recently, deep ultraviolet light having a wavelength of 193 nm is used. Also, although a theoretically highest value of the NA in atmosphere is 1, an immersion exposure apparatus in which the NA is increased to 1.35 by filling water between a projection lens and a substrate to be processed has been put to practical use in order to obtain a higher NA. Presently, to meet demands for further increasing the degree of micropatterning, extreme ultraviolet (EUV) lithography using EUV light having a wavelength of 13.5 nm as a light source is being examined.
On the other hand, imprint lithography is attracting attention as one of the next micropattern formation techniques (e.g., Jpn. Pat. Appln. KOKAI Publication Nos. 2007-81048, 2004-259985, and 2008-6638). Imprint lithography is a micropattern formation method. In this method, a substrate to be processed is coated with a photocurable imprinting agent, and this imprinting agent is pressed against a transparent mold having a desired uneven pattern. In this state, the imprinting agent is cured by emitting light from the mold side, and the mold is separated, thereby forming a desired pattern on the substrate.
Optical imprint lithography includes the step of coating a substrate to be processed with a photocurable imprinting agent, the (alignment) step of aligning this substrate with a light-transmitting mold, the step of bringing the mold into contact with the photocurable imprinting agent, the step of curing the photocurable imprinting agent by light irradiation in this state, and the (separation) step of separating the mold from the cured photocurable imprinting agent (resist pattern).
In imprint lithography, the alignment is finely adjusted by shrinking (deforming) the pattern of a mold by applying a force to the side surfaces of the mold by using actuators. If the force is not evenly applied to the mold, the way the force is applied to the pattern of the mold changes from one place to another, and no intended pattern is obtained. In addition, since the force is applied to the mold, the mold deforms while imprinting is repeated, and this changes the way the force is transmitted. Accordingly, the force that is initially evenly applied to the mold pattern is biased to a certain region of the mold pattern. This limits the life of the mold to the time at which mold deformation is no longer allowable.
As described above, the force is applied to a mold in use. To increase the accuracy of alignment and detect the life of the mold, therefore, the internal stress of the mold must be measured. However, the internal stress of the mold is difficult to measure.